The present invention relates to a vehicular automatic transmission and apparatus and method for controlling a gear shift of the vehicular automatic (power) transmission, especially, for controlling the gear shift of the vehicular automatic transmission so as to advance a suitable gear shift operation during a torque phase with no temporary neutral state.
An automatic transmission includes gear shifting frictional elements having a plurality of clutches and brakes. The gear shifting frictional elements are selectively and hydraulically (liquid pressure) operated (clutched) so as to determine a power transmission route (gear shift range) in a gear transmission system.
In addition, a switching between the operated frictional elements permits a gear shift from the present gear shift range to another gear shift range.
It is noted that, when the gear shift occurs, one of the frictional elements which is to be switched from a clutched (engaged) state to a released (de-clutched or disengaged) state is, hereinafter, referred to as a releasing (side) frictional element, its working liquid pressure is referred to as a releasing working liquid pressure, another of the frictional elements which is to be switched from the released state to the clutched state is referred to as a clutching (side) frictional element, and its working liquid pressure is referred to as a clutching working liquid pressure.
The automatic transmission is so constructed that the gear shift carried out by, so-called, an interchange (or shift) of the frictional elements such that while a certain frictional element is released due to a reduction in the working liquid pressure, the other frictional element is clutched due to an increase (rise up) of the working liquid pressure is present.
Unless both of the reduction in the working liquid pressure of the releasing frictional element(namely, the releasing working liquid pressure) and the increase in the working liquid pressure of the clutching frictional element (namely, the clutching working liquid pressure) are advanced with a suitable correlation in a case where the interchange of the frictional elements is carried out during the occurrence of the gear shift, a gear shift quality would be worsened such that a large torque absorption during a torque phase would be developed, a temporary engine idling with an accelerator pedal depressed at a preceding stage to the automatic transmission would be developed, and an elongated gear shift time duration would occur.
A Japanese Patent Application First Publication No. Heisei 4-175576 published on Jun. 23, 1992 exemplifies a first previously proposed gear shift control apparatus for an automatic transmission.
In the first previously proposed gear shift controlling apparatus for the automatic transmission, the releasing working liquid pressure is once below a required clutching capacity for the releasing frictional element so that the releasing frictional element is slipped, thus a slight engine idling with the accelerator pedal depressed, and a feedback control of the releasing working liquid pressure is carried out so that a variable corresponding to the engine idling described above becomes coincident with a target variable. However, since the feedback control of the releasing working liquid pressure such that the variable corresponding to the engine idling described above becomes coincident with the target variable means such a control as to make the associated engine to be idle with the accelerator pedal depressed, it is difficult to expect a sufficient improvement in the gear shift quality.
In addition, since, in the first previously proposed control apparatus, a system high responsive characteristic including a detection response of the engine idling and an operation response of an actuator is indispensable for the feedback control during a short torque phase.
Furthermore, it is difficult to put the above-described feedback control into practice with a practical difficulty in a high responsive characteristic to meet a demand as described above or with a high cost required in mind.
Next, a Japanese Patent Application First Publication No. Heisei 5-157168 published on Jun. 22, 1993 exemplifies a second previously proposed gear shift control apparatus for the automatic transmission.
In the second previously proposed gear shift controlling apparatus, a command to reduce the releasing working liquid pressure and a command to increase the clutching working cylinder are outputted in a manner such that a constant inverse proportional relationship is established between both liquid pressures so that the reduction in the releasing working liquid pressure is advanced in the constant inverse relationship with respect to the increase in the clutching working liquid pressure.
In the previously proposed gear shift controlling apparatus, a command to reduce the releasing working liquid pressure and a command to increase the clutching working cylinder are outputted in a manner such that a constant inverse proportional relationship is established between both liquid pressures so that the reduction in the releasing working liquid pressure is advanced in the constant inverse proportional relationship with respect to the clutching working liquid pressure.
However, since, when the clutching frictional element is clutched, the clutching of the frictional element is started after a large quantity of the working liquid is supplied to a working piston, the start of clutching of the clutching frictional element cannot avoid tending to be delayed with respect to the command issued to rise the clutching working liquid pressure.
Whereas, the reduction in the releasing working liquid pressure has not a noticeable delay with respect to a command to reduce the releasing working liquid pressure. The start of releasing of the releasing frictional element may be almost instant to the command to reduce the releasing working liquid pressure.
When the gear shift carried out by the interchange between the frictional elements such that the releasing frictional element is released (declutched) while the clutching frictional element is clutched, there is a tendency such that the release of the releasing frictional element would be started in prior to the start of the clutching of the clutching frictional element only if the command to reduce the releasing working liquid pressure and to the command to increase (rise) the clutching working liquid pressure are outputted with the constant inverse proportional relationship.
In this case, when the release of the releasing frictional element is carried out a torque charging of the releasing frictional element gives zero, the clutching of the clutching frictional element is not yet started.
Hence, the torque charging of the clutching frictional element is not yet carried out. As a result of this, the engine associated with the automatic transmission becomes idle with the accelerator pedal depressed.
The engine idling described above develops the torque absorption during the torque phase and the gear shift quality of the automatic transmission is remarkably reduced.
Upon the detection of the engine idling described above, the clutching of the clutching frictional element is started.
This raises the same problem as described in the first previously proposed gear shift controlling apparatus for the automatic transmission.
It is noted that with the delay in the start of clutching of the clutching frictional element with respect to the command to rise the clutching working liquid pressure taken into a previous consideration, the command to reduce the releasing working liquid pressure may be delayed with respect to the command to rise the clutching working liquid pressure. However, the delay in the start of the clutching of the clutching frictional element has an inherent difference between each automatic transmission.
In addition, since a continuous change in the delay in the start of clutching occurs due to an aging effect and/or an environmental change, an elimination of the engine idling described above cannot be assured.